Table of Contents

Introduction

Hazardous gases on farms can be found in silos, manure storages,
anaerobic digesters, grain bins and improperly ventilated barns
 structures that provide a confined space in which gases
can accumulate to dangerous levels or deprive the air of enough
oxygen to sustain life. Plant material stored in a silo ferments,
allowing the crop to be stored for a long time. However, the fermentation
process uses up oxygen, produces carbon dioxide and, under certain
conditions, nitrogen dioxide, as by-products. This results in
an environment unsuitable for humans soon after the silo is filled,
lasting for up to 2 weeks.

Manure that is stored for a long time undergoes anaerobic decomposition,
which produces manure gases. Warm weather and poor ventilation
can increase the concentration of these gases. Liquid manure tanks
can contain toxic levels of gases or can be devoid of oxygen.
High hydrogen sulphide gas levels can also deteriorate exposed
concrete above the liquid manure surface.

This Factsheet focuses on dangerous gases found around farm operations
and the safety precautions required to protect farm workers.

Hydrogen Sulphide

Hydrogen sulphide (H2S) is the most dangerous of the
manure gases. It is classified as a chemical asphyxiant because
it immediately chemically interacts with the blood's hemoglobin
to prevent oxygen from being carried to the body's vital organs
and tissues. It is produced from the anaerobic decomposition of
organic materials such as manure. Its characteristic rotten egg
smell is easy to detect at low concentrations, but at higher concentrations,
H2S paralyzes the sense of smell. In high concentrations,
hydrogen sulphide causes instant paralysis and death.

Table 1. Hydrogen sulphide effects
on humans at various concentrations

Table 1 outlines the effect of hydrogen sulphide
at various concentrations. Hydrogen sulphide is heavier than air,
therefore, it tends to stay just above the surface of the manure.
Ventilation systems and wind effects can cause the gas to move
up into the barn space towards an exhaust fan or open window.
The release of hydrogen sulphide is relatively low when manure
remains undisturbed and the outside temperature is low. However,
hydrogen sulphide levels can reach dangerous levels in seconds
when a tank is agitated, especially if splashing or surface agitation
takes place (Figure 1). Extra precautions are
required when dealing with an under-floor manure storage (see
Management Suggestions  Manure Storages). Several deaths have
occurred when workers have entered manure storages or the room
above one in an attempt to save someone who had been overcome
by H2S.

Hydrogen sulphide gas is a major concern for agricultural biogas
systems. It can be present in many structures related to the production
and consumption of biogas and can contain other hazardous gases.
For management options of hydrogen sulphide in agricultural biogas
systems, consult the OMAF and MRA Factsheet, Hydrogen
Sulphide in Agricultural Biogas Systems, Order No. 11-049.

Methane

Methane (CH4) is a colourless, odourless, non-toxic
but combustible gas, generated by anaerobic digestion of organic
material. If stored and managed properly, it can be used as a
fuel source for internal combustion engines or cleaned and injected
in the natural gas grid. It is lighter than air and therefore
tends to rise from the manure storage. In well-ventilated livestock
buildings, methane is unlikely to cause problems, however, in
covered and in-barn storages, methane can become trapped, and
the concentration can reach dangerously explosive levels.

Agitating manure in a liquid storage results in a rapid increase
in the release of manure gases and methane. If allowed to accumulate
in an enclosed space, methane gas can cause explosions. Improperly
designed plumbing pipes in staff rooms can also accumulate explosive
levels of methane. For example, floor drains must be equipped
with water traps to prevent migration of methane from the manure
storage back into the staff room.

Clause 78, Part VIII, in Ontario Regulation 267/03, created under
the Nutrient Management Act, 2002, requires that all new liquid
manure storages provide some form of ventilation to prevent the
accumulation and/or intensification of corrosive, noxious or explosive
gases.

The American Society of Agricultural and Biological Engineers
provides guidance for the management of hazardous gases with two
published standards:

Both standards offer management options to minimize the risks
 asphyxiation, poisoning and explosions  to humans
and livestock exposed to manure gases when entering confined-space
manure storages and to minimize the potential for drowning at
manure storage sites.

A series of incidents in North America involving fires in hog
barns caused by dangerous levels of methane have been a major
concern lately. For more information on the causes and management
practices of fires in hog barns, review the OMAF and MRA Factsheet,
Methane Gas in Hog Barns, Order No. 13-029.

Ammonia

Ammonia (NH3), a colourless gas with a characteristically
pungent odour, is produced by the decomposition of nitrogen compounds
in animal manures. Classified as an irritant, this gas is lighter
than air and can predispose livestock to various respiratory diseases
if they are exposed to a significant level for an extended period
of time.

Ammonia irritates the eyes at levels in the range of 2050 PPM,
depending on the sensitivity of the person or animal. This gas
is likely to be found mainly in swine, poultry and rabbit buildings,
however, it can also be a problem in manure composting operations.
As a guideline, if livestock or humans develop irritated eyes,
improve the ventilation in the building.

Carbon Dioxide

Carbon dioxide (CO2) is colourless and odourless.
It is, in part, the product of respiration of both plant material
and animals, and is found naturally in the atmosphere. Open-flame,
non-vented space heaters will also contribute carbon dioxide to
the surrounding air space, as one of the products of combustion.
CO2 is heavier than air and, like hydrogen sulphide,
will tend to accumulate just above the animal pen floor, surface
of manure in a manure tank or silage surface in a silo. The main
danger with carbon dioxide is that it can create an oxygen deficiency,
resulting in asphyxiation or suffocation. Properly ventilated
livestock buildings do not generally contain dangerous levels
of CO2, however, lethal concentrations can be found
in sealed silos, liquid manure storages and grain storages.

As part of the ensiling process, living plant material quickly
uses up available oxygen and dies. During this respiration process,
oxygen is converted to water and CO2. Carbon dioxide
displaces the oxygen in a sealed silo, making this environment
unsuitable for humans without an external air supply.

Nitrogen Dioxide

Nitrogen dioxide (NO2) is a dangerous chemical asphyxiant
produced as a result of chemical reactions that take place almost
immediately after plant material is placed into a silo. Even short-term
exposure can result in sudden death. NO2 has a characteristic
bleach-like odour and may be visible as a reddish-brown haze.
It is heavier than air, so it will tend to stay just above the
silage surface. It may also flow down silo chutes and into feed
rooms.

Weather conditions and cultural practices will affect the amount
of nitrates in plant material, which in turn will set the stage
for the production of NO2 in the silo. For example,
a dry period during the growing season followed by abundant rainfall
will encourage a corn crop to take up high levels of dissolved
nitrates. If the corn is harvested before the nitrates can be
converted to proteins, nitrous oxide (N2O) and nitric
oxide (NO) are produced. Unstable NO combines with oxygen to form
deadly nitrogen dioxide.

When inhaled, NO2 dissolves in the moisture on the
internal lung surface to produce a strong acid called nitric acid.
Nitric acid burns the lung tissues, which is followed by massive
bleeding and death. Repeated exposure to lower concentrations
of NO2 will cause chronic respiratory problems, including
shortness of breath, coughing and fluid in the lungs.

Safe Gas Levels

The American Conference of Government Industrial Hygienists has
established maximum safe gas concentrations, or threshold limit
values, for an 8-hour work day and 40-hour work week for humans
(Table 2). Although threshold limit values have
not been established for animals, many researchers have suggested
that animal responses are likely similar to humans.

Gas Detection Monitors

All of these hazardous gases can be measured with appropriate
test equipment. Although much of the equipment is expensive and
requires periodic re-calibration, there are some very reasonably
priced gas detection tubes and handheld monitors commercially
available from safety and scientific supply stores.

The most economical approach is to monitor gases with reactor
tubes in which the gas changes the colour of a reactant and gives
a good estimate of its concentration. These reactor tubes can
be used with a calibrated pump to draw a measured sample of gas
through the tube and obtain the result within a few minutes. However,
to take an air sample, the person operating the pump must be present
in the confined space, exposing himself to the potentially hazardous
atmosphere.

These tubes are also available as passive dositubes that react
slowly when exposed to the environment containing the gas of interest
and yield an average gas concentration over time. Depending on
the gas, the required exposure time would vary from several hours
to as much as 2 days.

Commercial handheld monitors available from safety and scientific
supply stores can also measure hazardous gases (Figure
2). Handheld detectors monitor environmental gases constantly,
are compact in size and sound an alarm when a dangerous gas level
is detected. They can be equipped with a sampling hose and pump
used to monitor the atmosphere of a confined space outside harm's
way. When purchasing a gas monitor, note whether the unit can
be calibrated at the farm or has to be serviced. Certain units
will stop working if the calibration has expired.

Operating the calibrating equipment requires minimal training.
The monitors cost from $250$400 for one gas; multi-gas monitors
equipped with a pump may cost up to $1,000. An alternative to
purchasing the equipment is to rent the unit (for a week or two)
and the appropriate personal protective equipment from a specialized
safety supply store. Specialized stores provide training services
with rental equipment or are in contact with local training providers.
The key is to plan ahead if the farming operation requires personal
protective equipment.

Management Suggestions

Manure Storages

Ensure covered manure storages are ventilated by some means
to prevent the accumulation of all hazardous gases.

Always maintain at least 0.3 m (1 ft) of freeboard between
the manure surface and the bottom of the slats to prevent animals
from routinely breathing hydrogen sulphide and carbon dioxide.

Post a "Danger, Deadly Gases" warning sign in a visible location
near each pump-out station.

Do not agitate the liquid manure in storage unless absolutely
necessary. If agitation is necessary, keep the agitator below
the liquid surface and do not direct the stream of agitated
manure towards a post or wall. Research has shown that gas levels
will increase to lethal levels in seconds when splashing or
surface agitation takes place (Figure 1).
Remove all livestock, if possible, before agitating and emptying.
Monitor gas levels in the barn.

If the barn has under-floor (pit) ventilation and the porosity
of the slatted floor is such that an air velocity through the
slats of at least 0.10 m/sec (20 ft/min.) can be obtained,
use the pit ventilation system. Ensure that any openings such
as pump-out ports are sealed off. For the pump-out port, this
might require the use of a piece of plywood or flexible skirt
to fit around the tractor-driven pump. This will maximize the
amount of air being drawn from the room down through the slats.
If gas detection equipment is available, monitor gas levels
in the barn.

If the barn does not have under-floor ventilation, or if
conditions are such that an air velocity down through the slats
of at least 0.10 m/sec (20 ft/min.) cannot be obtained, provide
maximum room ventilation. Be aware that there exists a greater
risk when there is no under-floor ventilation. Do not enter
the barn during or immediately following pumping or agitation.
If gas detection equipment is available, monitor gas levels
in the barn.

It is highly recommended that a hydrogen sulphide gas monitor
with an alarm be used to monitor gas levels in the barn, whenever
this type of storage is agitated or emptied (Figure
2). In addition, consider taking hydrogen sulphide awareness
training, available from consultants in Ontario.

When flushing gutters, provide maximum ventilation. Do not
enter the barn during or immediately following flushing. If
gas detection equipment is available, monitor gas levels in
the barn.

Ideally, locate all pump-out openings outside the building
to eliminate the danger of working in a confined area. Surround
them with a safety railing.

Do not attempt to rescue an animal if it collapses during
pumping or agitation. Turn off the pump, provide maximum ventilation
and wait a reasonable time before entering the barn. Again,
if gas detection equipment is available, ensure a safe concentration
level prior to entering.

Avoid any source of ignition, such as smoking, in the barn
or near a manure storage facility. Avoid operating welding equipment
in confined spaces without testing and monitoring the atmosphere
and providing constant ventilation.

Covered manure storages, even when empty, should only be
entered by trained personnel equipped with suitable self-contained
breathing apparatus. Never assume that gas levels are safe.

If a rescue becomes necessary, call your local fire department.
Do not attempt a rescue on your own.

If you suspect that you have been exposed to high levels
of manure gas, consult your physician or the anti-poison centre
immediately.

Inspect the safety fence periodically to ensure there are
no openings and that warning signs are still in place.

Ensure that modifications to the ventilation system or any
reconfiguration of the livestock building do not affect the
venting of hazardous gases in under-barn manure storages. Consult
an agricultural engineer when making structural or ventilation
modifications where an under-barn manure storage is present.

Liquid Manure Tankers

Never assume a tanker is safe to enter, even when empty.
Hydrogen sulphide, which is heavier than air, will collect at
the bottom of the tanker and remain there, even though there
is an opening at the top. In August 2000, three men lost their
lives during an attempted repair of a manure tanker and the
subsequent rescue effort. Never enter a liquid manure tanker
unless you are equipped with suitable self-contained breathing
apparatus.

When working around liquid manure storages and tankers, farm
workers can protect themselves by wearing a pocket-sized hydrogen
sulphide monitor that will sound an alarm when dangerous gas
levels are reached.

Newer liquid tankers are equipped with safety hatches to
prevent unauthorized entry. However, a large number of older
units in use across Ontario do not have a safety hatch. Retrofit
these tankers with a safety hatch on the top opening to prevent
unauthorized entry. These safety hatches can be purchased from
a number of farm equipment dealers or can be custom made. Figure
3 shows an example safety hatch.

Figure 3. Safety
hatch for liquid manure tanker.

Silos

Post a "Danger, Deadly Gases" warning sign in a visible location
near the silo.

Do not allow children or visitors near the silo for 3 weeks
after filling.

Provide sufficient feed room ventilation to exhaust any silo
gas that might have spilled down from the silo.

Check with your local fire department to see if pressure-demand
remote breathing apparatus is part of their emergency equipment.
Self-contained breathing apparatus (i.e., scuba) equipment is
not suitable because of the air tank. It is sometimes too big
for climbing the silo chute or the outside ladder-cage or too
small to contain enough reserve air to rescue someone.

During filling, adjust the distributor as needed to level
the silage. Do not level the material by hand.

If it is necessary to enter the silo when filling is complete,
do so immediately following the last load, on the same day.
Remember to leave the blower running while inside.

Oxygen-limiting silos are a special case and should never
be entered. If it becomes absolutely necessary to enter such
a silo, it is essential that an external air supply be worn
and back-up emergency safety measures are in place. Consult
publication I33 Alert: Atmospheric Hazards Associated with Oxygen-Limited
Structures (Silos) on Farms, by the Ministry of Labour, for
suggested precautions.

A top unloader can ventilate a silo effectively. However,
if it becomes necessary to service a defective unloader, assume
that gases are present. To expel gases before entering, run
the forage blower with the chute doors closed and the roof vent
open. If the head space is greater than 5 m (15 ft), attach
a tube adapter to the blower pipe (Figures 4
and 5). For a 7.2-m (24-ft) diameter
silo with 510 m (1530 ft) of head space, let the blower
run for 30 min. For larger diameter silos or silos with
a deeper head space, increase the ventilation time. Leave the
forage blower running while in the silo.

If someone collapses inside a silo, begin ventilating with
the forage blower immediately, as explained above, and contact
your local fire department. A fresh air supply is critical for
both the victim and rescuers. Never attempt to rescue someone
yourself. This has been attempted many times and, without the
proper equipment and training, has resulted in many incidents
of multiple fatalities.

Farm Labour Concerns and Hazardous Gases

Since 2006, the Ontario Occupational Health and Safety Act applies,
with some limitations and conditions, to all farming operations
that have paid workers, under O. Reg. 414/05, Farming Operations.
It does not apply to a farming operation operated by a self-employed
person who does not have paid workers.

A recent hazard alert, I33 Alert: Atmospheric Hazards Associated
with Oxygen-Limited Structures (Silos) on Farms was published
by the Ministry of Labour following a recent fatality in Eastern
Ontario involving an unplanned entry in an oxygen-limited atmosphere.
The worker was overcome immediately after entering a silo by the
hazardous atmosphere. The hazard alert lists relevant legislative
requirements for employers and employees and suggested precautions
for entry in oxygen-limiting structures, such as training, supervision,
work procedures, signage, atmospheric monitoring, PPE (personal
protective equipment) and mechanical ventilation. In general,
the employer shall take every precaution reasonable for the protection
of a worker.

For a more complete overview of legislative requirements and
suggested practices, consult the Occupational Health and Safety
Guidelines for Farming Operations, published by the Ministry of
Labour, www.ontario.ca/labour
(Ministry of Labour Health and Safety Contact Centre, 1-877-202-0008).

Conclusion

Never assume that the environment inside a silo or manure storage
is safe. Do not enter a liquid manure tank or recently filled
silo, under any circumstances, without a pressure-demand remote
breathing apparatus. These confined spaces often contain lethal
concentrations of hazardous gases. Always have a lifeline attached,
with a responsible, trained and competent safety person in view
of your work. Follow the management suggestions outlined in this
Factsheet and the legislative requirements of the Occupational
Health and Safety Act. Post clearly visible warning signs to warn
others to stay away.

This Factsheet provides basic awareness information on hazardous
gases found on agricultural operations. This document does not
intend to provide assurance of compliance with occupational health
and safety regulations in Ontario. To receive local assistance
for compliance with the Occupational Health and Safety Act, call
Workplace Safety Prevention Services (formerly known as Farm Safety
Association), toll-free at 1-800-361-8855, if you are located
in Ontario.

Patni, N.K., and S.P. Clarke. 2003. Gaseous Emissions in Swine
Barns and During Slurry Mixing in Sub-Floor Pits. ASAE Meeting
Paper Number 034081. American Society of Agricultural and Biological
Engineers, St. Joseph, MI, U.S.

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